It is known that cycloolefins containing a norbornene moiety can be polymerized in the presence of an alkylaluminum halide cocatalyst and a molybdenum or tungsten halide catalyst. This is accomplished by mixing a cycloolefin with a solvent and charging the mixture to a reactor. A molecular weight modifier is charged to the reactor followed by cocatalyst and catalyst. The catalyst is added as a solution in an alkylester of a saturated carboxylic acid, since it is insoluble in the monomer. Polymerization is conducted by ring opening at 0.degree. to 200.degree. C. and is completed in less than 2 hours after shortstopping with an alcohol. The reaction product is a smooth, viscous material of a honey-like consistency comprising polycycloolefin dissolved in the solvent.
U.S. Pat. No. 4,380,617 to Minchak et al discloses the use of organoammonium molybdates and tungstates in the polymerization of cycloolefins. The organoammonium molybdate and tungstate catalysts are soluble in cycloolefins and therefore, do not require the use of an alkylester solvent, which caused problems in the prior art polymerization. Furthermore, since the catalyst is soluble in cycloolefins, polymerization of the cycloolefins in bulk is thereby facilitated.
Although the function of the catalyst is improved by using organoammonium molybdates or tungstates instead of molybdenum or tungsten halides, the cocatalyst is still too active and results in rapid polymerization of cycloolefins which is difficult to control. U.S. Pat. No. 4,426,502 discloses the use of alkoxy-aluminum halide or aryloxyaluminum halide cocatalysts. By introducing an alkoxy or an aryloxy group into the cocatalysts, it is thus possible to diminish the reducing power of the cocatalysts so that a controlled polymerization can be conducted. The use of such cocatalysts makes it possible to prepare a monomer mix at room temperature which is inactive and then to polymerize the monomer mix at an elevated temperature, as by injecting it into a pre-heated mold. It is particularly significant that diminishing the reducing power of the cocatalysts by this method does not retard the rate of polymerization in a real sense. This development makes it possible to polymerize cycloolefins in bulk or by reaction injection molding, which is a form of bulk polymerization.
Polycycloolefins have found numerous applications in the electronics industry, however, the presence of a halogen in the system cannot be tolerated since halogen can corrode or have other adverse electrical effects and render a circuit unreliable or inoperable. U.S. patent application entitled "Polymerization of Cycloolefins With Halogen-Free Cocatalysts" by inventors Minchak et al, discloses halogen-free cocatalysts which can be used with halogen-free catalysts in a halogen-free system to polymerize cycloolefins. The halogen-free cocatalysts are characterized by the use of an alkylaluminum, specifically trialkylaluminum, cocatalyst in conjunction with a modifier compound selected from trialkyl tin oxides, with or without a hindered phenol. The cocatalyst can also be devoid of a modifier compound in which instance, it includes a trialkylaluminum which is used together with a hindered phenol.